Zika struck Florida up to 40 times before detection

Photographer: James Gathany / CDC

With a newly-obtained blood meal visible through her transparent abdomen, a female Aedes aegypti mosquito takes flight as she leaves her host's skin surface. These mosquitoes can carry Zika and other viral diseases.

With a newly-obtained blood meal visible through her transparent abdomen, a female Aedes aegypti mosquito takes flight as she leaves her host's skin surface. These mosquitoes can carry Zika and other viral diseases. (Photographer: James Gathany / CDC)

Zika was circulating in the Americas long before the first reports arose about the virus that can cause the brain condition called microcephaly in fetuses, according to a series of international studies published Wednesday.

A key takeaway from the four studies, which reported more than 200 new Zika viral genomes, is that controlling the mosquito that carries Zika should be a high priority, along with detection programs that constantly monitor for the virus.

The same study also found that Miami and the Brownsville area of Texas have the best conditions for Zika establishing itself permanently. Their climates enable year-round survival of the Aedes aegypti mosquito, which carries Zika and other diseases.

Miami is especially vulnerable because of its travel connections to the Caribbean and Latin America. However, even in Miami, there were not enough secondary infections during the recent outbreak to establish Zika permanently.

The study was published in the journal Nature; it can be found at j.mp/tsrizika. Nathan Grubaugh, Karthik Gangavarapu and Kristian Andersen, all of Scripps Research, were among its authors.

Prevention by mosquito control is an excellent strategy, Andersen said in a Tuesday news conference held by Nature.

“What we show is that the number of human cases basically is perfectly correlated with the number of mosquitoes that you have in the area,” Andersen said. “So if the numbers of mosquitoes go up, you see the human cases going up. If the number of mosquitoes is going down, you see the number of human cases also going down.

“So that tells us that things like vector control, essentially focusing on actually getting rid of the mosquitoes, is an effective way of actually preventing human cases of Zika from occurring,” Andersen said.

Two other studies published in Nature showed that Zika circulated in Brazil for more than a year before the first case was reported. These analyses used a genome-sequencing lab, so they were able to detect and sequence strains of Zika out in the field. A family tree of these strains indicated that northeastern Brazil was the likely origin of the outbreak.

The fourth study, published in the journal Nature Protocols, describes a method used to sequence the Zika virus directly from samples, without the time-consuming process of growing tissue cultures. The report, which used DNA sequencing machines from Oxford Nanopore and the San Diego-based Illumina, can be found at j.mp/illuminaoxford.

A perspective article on all four studies proposes that such detection efforts be prepared in advance for rapid deployment when the next outbreak strikes. The studies make clear that Zika transmissions happen so often, and that it’s impossible to know which one will spark the next outbreak. The same may be true of other viral diseases.

These diseases can be regarded as biological wildfires, wrote Michael Worobey at the University of Arizona, a former forest firefighter. And just like wildfires, they can cause immense human suffering and financial damage.

“The responses to the recent Ebola and Zika outbreaks undoubtedly involved great courage and ingenuity, but they have looked too much like valiant bucket brigades organized after the fire is out of control,” Worobey wrote in the perspective article. “We should be detecting such outbreaks within days or weeks through routine, massive, sequence-based approaches — not months or years later, when clinical symptoms have accumulated.”

This vision is feasible now, Worobey wrote, thanks to the recent dramatic improvements in efficiency and lowered cost of genetic sequencing, combined with powerful computational methods.